Indications for a wave dependent Charnock parameter from measurements during ASGAMAGE

Eddy-correlation measurements of the wind stress and wave measurements were made during ASGAMAGE, an experiment carried out in 1996 at research platform Meetpost Noordwijk (MPN) in the southern North Sea. An analysis of the results confirms the predicted wave dependence of the Charnock parameter. As in HEXOS, an earlier experiment at the same platform, the corresponding values of the drag are higher than those found in the open ocean. We show that this is consistent with the existence of a wave-age dependent Charnock parameter and the fact that, for given wind speed, on average, wave ages are lower at MPN than in the open ocean.